Objective, especially a projection objective for microlithography

ABSTRACT

An objective is provided with a plurality of lenses, mirrors and at least one beam splitter element ( 20 ) inserted in an objective housing ( 1 ). One or more surfaces ( 26, 27, 28 ), situated in the beam path, of the beam splitter element ( 20 ) are provided as correction aspherics. The beam splitter element ( 20 ) can be provided with manipulators ( 22 ) that are arranged on a manipulator carrier ( 23 ) which is permanently connected to the objective housing.

The invention relates to an objective having a plurality of lenses,mirrors and at least one beam splitter element inserted in an objectivehousing. In particular, the invention relates to a projection objectivefor microlithography for producing semiconductor components.

Use is increasingly being made of so-called correction aspherics inorder to correct optical elements, in particular objectives for thesemiconductor industry such as, for example, projection objectives forproducing semiconductor elements. Thus, for example, it is known to usea correction aspheric near the object or an image field region of theobjective, and a correction aspheric near a pupil region. Aberrations inthe imaging accuracy, for example aberrations lying outside prescribedtolerances, can be corrected subsequently by means of the correctionaspherics. For this purpose, lenses selected correspondingly thereforare removed from the objective, their surfaces to be aspherized aremachined appropriately to yield a new desired and/or preselectedaspheric as correction aspheric in order to correct the aberrations inthe imaging accuracy. The lens thus machined with the correctionaspheric is subsequently reinserted into the objective housing. However,a precondition for this is that, after the reinstallation, the machinedoptical element is seated again exactly within its six degrees offreedom at the same point as before being removed. Moreover, the removaland installation is to be as simple as possible and also after it isreinstalled there must be the same deformation state of the machinedelement as was present before its removal.

If a plurality of correction aspherics are required in the objective,this entails a corresponding outlay.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide correctionaspherics in the objective which entail a low outlay, there being, inparticular, a simplification in their removal and subsequentinstallation.

According to the invention, this object is achieved by virtue of thefact that one or more surfaces, situated in the beam path, of the beamsplitter element are provided as correction aspherics, the beam splitterelement advantageously being connected to manipulators that are arrangedon a manipulator carrier which is permanently connected to the objectivehousing.

According to the invention, use is now made of a beam splitter elementto form correction aspherics.

A beam splitter element is to be installed exactly in an objective withreference to its position. If it is now also provided with manipulators,it can be removed and reinstalled with reference to its position in aspecifically repeatable fashion. It is also simultaneously possible tomaintain the deformation state in this case. If required, threetransmitting surfaces are available as correction aspherics owing to thefact that a beam splitter element, for example a beam splitter cube, hasa plurality of surfaces situated in the beam path, specifically theentry surface of the beam splitter element, an intermediate exit surfacesituated offset in relation thereto by an angle of 90° ±20° , and a rearexit surface, as seen in the beam direction. This means that, bycomparison with the known correction aspherics fitted on lenses, thereis a need to remove only a single part, specifically the beam splitterelement, after which it is possible to machine three differenttransmitting surfaces in case of need, and thus to undertake threedifferent corrections.

All that need be ensured in this case is that the beam splitter elementis provided with manipulators and sensors in such a way that exactly thesame position as obtained before removal can be recreated after theremoval and completed reinstallation so as to prevent new aberrationsbeing introduced into the objective.

In general, it will be sufficient to provide a possibility of pivotingthe beam splitter element about at least two axes that areadvantageously located in the beam splitter plane.

In this case, the tilt axes should intersect at a point, the aim being,in an advantageous embodiment of the invention, for the point ofintersection to be situated in the beam splitter plane in a centralregion in which the principle axis lies.

As a result of such an embodiment, no spatial displacements occur. Thatis to say, it is also possible, if required, to design the manipulatorssuch that the beam splitter element can be tilted about three axes, oneof the tilt axes lying in the beam splitter plane, and the two othertilt axes each lying, offset by 90° in relation thereto, at an angle of45° to the beam splitter plane.

Advantageous refinements and developments emerge from the exemplaryembodiment described in principle below with the aid of the drawing, inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustration of the principle of a projection exposuremachine having a projection objective with a beam splitter cubeaccording to the invention as beam splitter element,

FIG. 2 shows an enlarged illustration of the beam splitter cube fromFIG. 1, in side view, and

FIG. 3 shows a view of the beam splitter element from the direction ofthe arrow A in accordance with FIG. 2.

DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

FIG. 1 illustrates the principle of a projection exposure machine havinga projection objective 1 for microlithography, for the purpose ofproducing semi-conductor elements.

Said objective has an illuminating system 2 with a laser (notillustrated) as a light source. Located in the object plane of theprojection exposure machine is a reticle 3 whose structure is to beimaged on a correspondingly reduced scale onto a wafer 4 that isarranged below the projection objective 1 and is located in the imageplane.

The projection objective 1 is provided with a first, vertical objectivepart 1 a and a second, horizontal objective part 1 b. Located in theobjective part 1 b are a plurality of lenses 5 and a concave mirror 6,which are arranged in an objective housing 7 of the objective part 1 b.A beam splitter element 20 is provided in order to deflect theprojection beam (see arrow) from the vertical objective part 1 a with avertical optical axis 8 into the horizontal objective part 1 b with ahorizontal optical axis 9.

After reflection of the beams at the concave mirror 6 and subsequentpassage through the beam splitter element 20, these strike a deflectingmirror 11. At the deflecting mirror 11, the horizontal beam path 9 isdeflected in turn to a vertical optical axis 12. Located below thedeflecting mirror 11 is a third, vertical objective part 1 c with afurther lens group 13. Also additionally located in the beam path arethree λ/4 plates 14, 15 and 16. The λ/4 plate 14 is located in theprojection objective 1 between the reticle 3 and the beam splitterelement 20 downstream of a lens or lens group 17, and in each casevaries the direction of polarization of the beams by 90° . The λ/4 plate15 is located in the beam path of the horizontal objective part 1 b, andthe λ/4 plate 16 is located in the third objective part 1 c. The threeλ/4 plates serve the purpose of changing the polarization during passagethrough the projection objective 1 such that the same direction ofpolarization again obtains on the output side as on the input side, as aresult of which, inter alia, beam losses are minimized.

The beam splitter element 20 from FIG. 1 is explained in more detail inan enlarged illustration in FIGS. 2 and 3. The beam splitter element 20is arranged on an intermediate support 21 for the purpose of deformationdecoupling. Manipulators 22 (not illustrated in more detail) act on theintermediate support 21 and are supported on a manipulator carrier 23.The manipulator carrier 23 is connected to a part of the objectivehousing 1 b of the projection objective via tuning disks 24 that serveto adjust the beam splitter element 20 for the first time.

The beam splitter element 20 has 3 optically active surfaces that aresituated in the beam path. These are an entry surface 26, which issituated in the beam path between the lens 17 and the beam splitterelement 20, an intermediate exit surface 27, which is situated in thebeam path of the horizontal objective part 1 b of the projectionobjective 1 with the lenses 5 together with the deflecting mirror 6 andλ/4 plates 15, and an exit surface 28 of the beam splitter element thatis directed toward the deflecting mirror 11.

In a well known manner, the effect of the beam splitter element 20 inconjunction with the λ/4 plates 14 and 15 is a deflection into thehorizontal objective part 1 b comprising the mirror 6 and the lenses 5of the projection objective 1. This detection takes place at the beamsplitter plane 29 being inclined by 45° ±10° to the incident beam path,of the beam splitter element 20 owing to the λ/4 plate 15 located inthis beam path, the beam path reflected by the mirror 6 now penetratesthe beam splitter plane 29 and exits at the exit surface 28 of the beamsplitter element 20.

This means that three surfaces are available for forming correctionaspherics at the beam splitter element 20, specifically the entrysurface 26, the intermediate exit surface 27 and the exit surface 28.

If, after installation of all the optical elements in the projectionobjective 1, it is established that corrections are required to increasethe imaging accuracy, the beam splitter element 20 is removed and, inaccordance with the correction requirements, individual surfaces, or allthree of the available surfaces situated in the beam path, arecorrespondingly provided with correction aspherics. This is followed byrenewed installation.

In order, now, to carry out this renewed installation as exactly aspossible and to reinstall the beam splitter element 20 with appropriateaccuracy in the position that it had, the manipulators 22 must bedesigned and moved appropriately. At the same time, this means that itmust be possible to pivot the beam splitter element 20 at least abouttwo axes. The two axes are the x- and y-axes, the x-axis being locatedin the beam splitter plane 29, and the y-axis being inclined at 45°thereto, as a result of which it is also situated at the same timeparallel to the optical axis in the exit region.

In addition, for adjusting purposes, it is also possible, to be precise,to include the z-axis as a third tilt axis that is situated offset by90° in relation to the two other axes and at an angle of 45° to the beamsplitter plane 29, as a result of which it is also situated parallel tothe optical axis in the entry region.

In this case, the three tilt axes, the x-, y- and z-axes, are tointersect at a point that is located in the beam splitter plane 29 inthe central region, in which the principal axis also lies. This point isdenoted by “30” in FIGS. 2 and 3.

Sensors and reference surfaces are correspondingly required for thepurpose of adjusting the beam splitter element 20. As is illustrated inFIGS. 2 and 3, these can be capacitive sensors 31 a, 31 b, 31 c, 31 d,31 e and 31 f. The sensors “31 a to 31 f ” cooperate in a known way withreference surfaces 32 that are located on the beam splitter element 20.The capacitive sensors 31 a and 31 b are situated without making contactat a spacing from one another upstream of the entry surface 26. Thesensor 31 c is located without making contact upstream of theintermediate exit surface 27, and the sensors 31 d, e and f are situatedon one side of the beam splitter element 26, being situated parallel tothe horizontally running beam path and at right angles both to the entrysurface 26 and to the intermediate exit surface 27 and the exit surface28.

The manipulators 22 can be of any desired design. The only importantpoint is that they be designed such that the beam splitter element 20can be tilted about at least two, preferably three, tilt axes. Thus, forexample, the intermediate support 21 can be connected by a universaljoint via the manipulators 22 to the manipulator carrier 23. Thearticulated joints for this purpose can be designed as solid joints,since these make possible displacements that are very exact andreproducible.

1-9. (canceled)
 10. An objective comprising a plurality of lenses,mirrors and at least one beam splitter element inserted in an objectivehousing, wherein one or more surfaces located in the beam path, of saidbeam splitter element are provided as correction aspherics.
 11. Theobjective as claimed in claim 10, wherein said beam splitter element isconnected to manipulators that are arranged on a manipulator carrierwhich is permanently connected to the objective housing.
 12. Theobjective as claimed in claim 10, wherein provided as correctionaspherics are an entry surface of said beam splitter element, anintermediate exit surface of said beam splitter element, located offsetin relation to said entry surface, and a rear exit surface, as seen inthe beam direction, of said beam splitter element.
 13. The objective asclaimed in claim 12, wherein said beam splitter element can be tiltedabout at least two axes.
 14. The objective as claimed in claim 13,wherein the tilt axes intersect at a point.
 15. The objective as claimedin claim 14, wherein said point of intersection is located in the beamsplitting plane of said beam splitter element in a central region inwhich the principal axis is located.
 16. The objective as claimed inclaim 13, wherein said beam splitter element is tiltable about threeaxes, one of the tilt axes being located in the beam splitting plane,and the two other tilt axes each being located, offset by 90° inrelation thereto, at an angle of 45° to the beam splitting plane. 17.The objective as claimed in claim 11, wherein for the purpose ofdeformation decoupling of said beam splitter element an intermediatesupport on which said beam splitter element is arranged and on whichsaid manipulators act, is provided.
 18. The objective as claimed in oneof claims 10 to 17, wherein it is a projection objective formicrolithography for producing semiconductor components.
 19. Anobjective comprising a plurality of optical elements inserted in anobjective housing, and at least one beam splitter element, wherein saidbeam splitter element is provided with manipulators, and wherein one ormore surfaces, located in the beam path, of said beam splitter elementare provided for processing as correction aspherics.
 20. The objectiveas claimed in claim 19, wherein said manipulators are arranged on amanipulator carrier which is permanently connected to the objectivehousing.
 21. The objective as claimed in claim 19, wherein provided ascorrection aspherics are an entry surface of said beam splitter element,an intermediate exit surface of said beam splitter element, situatedoffset in relation to said entry surface, and a rear exit surface, asseen in the beam direction of said beam splitter element.
 22. Theobjective as claimed in claim 21, wherein said beam splitter element istiltable by said manipulators about at least two axes (x,y).
 23. Theobjective as claimed in claim 22, wherein the tilt axes intersect at apoint.
 24. The objective as claimed in claim 23, wherein said point ofintersection is located in the beam splitting plane of said beamsplitter element in a central region in which the principal axis islocated.
 25. The objective as claimed in claim 22, wherein said beamsplitter element is tiltable by said manipulators about three axes, oneof the tilt axes (x) being located in the beam splitting plane, and thetwo other tilt axes each being located, offset by 90° in relationthereto, at an angle of 45° to the beam splitting plane.
 26. Theobjective as claimed in claim 20, wherein provided for the purpose ofdeformation decoupling of said beam splitter element is an intermediatesupport on which said beam splitter element is arranged and on whichsaid manipulators act.
 27. A projection objective for microlithographyfor producing semiconductor components, comprising optical elementsinserted in an objective housing, and at least one beam splitterelement, wherein said beam splitter element is provided withmanipulators, and wherein one or more surfaces, located in the beampath, of said beam splitter element are provided for processing ascorrection aspherics.
 28. The projection objective as claimed in claim27, wherein said manipulators are arranged on a manipulator carrierwhich is permanently connected to the objective housing.
 29. Theprojection objective as claimed in claim 27, wherein provided ascorrection aspherics are an entry surface of said beam splitter element,an intermediate exit surface of said beam splitter element, locatedoffset in relation to said entry surface, and a rear exit surface, seenin the beam direction of said beam splitter element.
 30. The projectionobjective as claimed in claim 29, wherein said beam splitter element istiltable by said manipulators about at least two axes (x,y).
 31. Theprojection objective as claimed in claim 30, wherein the tilt axes(y,x,z) intersect at a point.
 32. The projection objective as claimed inclaim 31, wherein said point of intersection is located in the beamsplitting plane of said beam splitter element in a central region inwhich the principal axis is located.
 33. The projection objective asclaimed in claim 30, wherein said beam splitter element is tiltable bysaid manipulators about three axes, one of the tilt axes (x) beinglocated in the beam splitting plane, and the two other tilt axes (y, z)each being located, offset by 90° in relation thereto, at an angle of45° to the beam splitting plane.
 34. The projection objective as claimedin claim 27, wherein provided for the purpose of deformation decouplingof said beam splitter element is an intermediate support on which saidbeam splitter element is arranged and on which said manipulators act.35. A system for correcting imaging aberrations in a projectionobjective for microlithography for producing semiconductor components,comprising a plurality of optical elements inserted in an objectivehousing, and comprising at least one beam splitter element, one or moresurfaces, located in the beam path, of said beam splitter element beingused as correction aspherics in such a way that if imaging aberrationsare found said beam splitter element is removed, said one or moresurfaces located in the beam path are processed, and said beam splitterelement is subsequently reinstalled.
 36. The system as claimed in claim35, wherein said at least one beam splitter element is provided withmanipulators that align said beam splitter element in the objectivehousing.
 37. The system as claimed in claim 35, wherein the imagingaccuracy of a projection beam is measured, and one or more surfaceslocated in the beam path are corrected by using the measurement resultin the state with the objective housing removed, and said beam splitterelement is subsequently reinstalled in the objective housing.
 38. Thesystem as claimed in claim 37, wherein the correction method of saidsurfaces is carried out in a number of steps.
 39. The system as claimedin claim 35, wherein used as correction aspherics are an entry surfaceof said beam splitter element, an intermediate exit surface of said beamsplitter element, situated offset in relation to said entry surface, anda rear exit surface, as seen in the beam direction of said beam splitterelement.
 40. The system as claimed in claim 36, wherein said beamsplitter element is tilted by said manipulators about at least two axes(x,y).
 41. The system as claimed in claim 40, wherein the tilt axes(y,x,z) intersect at a point.
 42. The system as claimed in claim 41,wherein said point of intersection is located in the beam splittingplane of said beam splitter element in a central region in which theprincipal axis is located.
 43. The system as claimed in claim 40,wherein said beam splitter element can be tilted by said manipulatorsabout three axes, one of the tilt axes (x) being located in the beamsplitting plane, and the two other tilt axes (y, z) each being located,offset by 90° in relation thereto, at an angle of 45° to the beamsplitting plane.
 44. The system as claimed in claim 35, wherein providedfor the purpose of deformation decoupling of said beam splitter elementis an intermediate support on which said beam splitter element isarranged and on which said manipulators act.